Answer: Earth is an open system because heat energy from the Sun enters through the atmosphere.
Explanation:
There are three types of system:
1. Isolated system: A system in which neither energy nor matter is exchanged with the surroundings.
2. Open system: A system in which both energy and matter is exchanged with the surroundings.
3. Closed system: A system in which only energy but not matter is exchanged with the surroundings.
Thus as heat energy from the sun is absorbed by the earth and then is radiated back, it is an example of open system.